1. Field of the Invention
The invention concerns the control of several actuators, and more specifically the electronic devices for controlling several actuators.
2. Description of the Related Art
Such control devices are in particular used to control the sequential movement of needles of several injectors between an injection position and a closure position. The duration over which the needle is no longer in the closure position defines its duration of injection. To provide optimum operation of an internal combustion, it is desirable for the injection duration to be substantially identical in each cylinder of the engine.
An integrated circuit is presently marketed under the reference TLE 6244 by the company Infineon. This integrated circuit controls all the injectors of a combustion engine. This circuit has one control stage per injector. FIG. 1 schematically illustrates the control stage for an injector of this circuit. The load formed by an injector is illustrated by the inductance 11. The vehicle's battery voltage Vbr is applied to one of its terminals. Its other terminal is connected to the drain of a P-channel MOSFET transistor 12. The source of the MOSFET 12 is connected to ground. A Zener diode 13 and a diode 14 are connected between the drain and the gate of the transistor 12. The gate receives signals for controlling a controller which is not illustrated.
The control stage illustrated operates as follows:
The gate of the MOS is activated by the high state of the control signal. The MOS then becomes conducting and its drain voltage changes substantially from the voltage Vbr to zero voltage. When the control signal changes to the low state, the MOS then becomes blocked. Due to the rapid cutoff of the MOS, the inductance generates a rapid rise in the MOS drain voltage. When the drain voltage reaches the Zener voltage of the diode 13, the MOS is made conducting again and the drain voltage is held at the Zener voltage for a predetermined duration of discharge of the inductance. The amplitude of the Zener voltage defines the instant of closure of the needle associated with the inductance.
This control device exhibits drawbacks. Specifically, to obtain injection durations that are as similar as possible for the various cylinders, this control device imposes very tight tolerance limits on the electronic components. The cost of the electronic components used, and in particular the Zener diodes, is therefore high.
Furthermore, when several control stages are integrated in the same circuit, the tolerance obtained when the circuits are produced may remain acceptable. When at least two independent circuits are used to control the various injectors, the tolerance obtained by producing the circuits becomes inadequate.
Therefore a need exists which the invention aims to satisfy for a control device overcoming one or more of these drawbacks.